Method of charging and exposing electrophotographic plates



IN VEN TORS Patented Feb. 27, 1951 METHOD OF CHARGING AND EXPOSING ELECTROPHOTOGRAPHIC PLATES Charles D. Oughton, Worthington, and William E. Bixby, Columbus, Ohio, assignors, by mesne assignments, to The Haloid Company, Rochester, N. Y., a corporation of New York Application December 6, 1948, Serial No. 63,778

3 Claims.

This invention relates to a method and apparatus for electrostatically charging and exposing an electrophotographic plate having a photoconductive insulating surface, such as used in electrocopying where a plate with a photoconductively sensitized surface is electrostatically charged and exposed to form an electrostatic image that is dusted with electroscopic powder and the powder image transferred to a paper or other support and'aflixed thereto, and it has for its purpose to afford a simple and effective method that enables performing the charging and exposing operations simultaneously.

Heretofore the usual practice has' been to charge the electrophotographic plate with elec-v trostatic charging mechanism in one operation and subsequently expose the charged plate to light While in another position in a light-projecting cabinet, and the present invention has for its purpose to aiford a method and apparatus whereby the charging and exposing operations can be carried on at the same time and without changing the positions of the plate and copy sheet.

More particularly the invention has for its purpose to enable electrostatically charging a plate through a copy sheet or original positioned thereon, such charge being applied successively to different portions of the plate and each said portion being exposed to light immediately after being charged, the charging and light-projecting operations taking place simultaneously, and successively on given areas of the plate.

To these and other ends the invention consists in the method and construction that will appear clearly from the following description when read in conjunction with the accompanying drawings, the novel features being pointed out in the claims following the specification.

In the drawings:

Fig. 1 is a diagrammatic plan view illustrating one practical embodiment of a construction for carrying out the invention, and

Fig. 2 is a longitudinal vertical sectional view of the same.

In making electrophotographic copies with a plate having a surface that is sensitized with a layer of selenium or other suitable material to afford a photoconductive insulating surface on a conductive backing, the usual practice has been first to charge the sensitive insulating surface electrostatically and after the plate is electrostatically charged, it is placed in a light cabinet or otherwise exposed to light projected through the copy sheet.

This requires two separate mechanisms and operations, whereas according to the present invention, these two operations are performed simultaneously and to accomplish this, there is provided a combination electrostatic charging and light-projecting mechanism which includes conducting bar I, provided with charging elements such as corona discharge needles 2, and connected with any suitable source of high potential current. supply, these arts being mounted on a suitable frame or support 3, which carries an electric lamp spaced from the bar I as shown at l. The bar l, needles 2, and lamp 4 extend across the electrophotographic plate and copy sheet to be described presently from one edge to the other, while 5 designates a suitable lens element also coextensive with the plate crosswise, and acting to transmit the light from the line filament or other source into a narrow band extending across the electrophctographic plate and copy sheet. The lamp 4 may be an incandescent electric lamp having a fine line filament, or any other source of light suitable for the purpose.

The electrophotographic plate comprises a conductive plate 6 provided with the photoconductive insulating layer or sensitized surface I, while 8 designates the copy sheet or original to be reproduced, which is positioned on the photoconductive insulating surface of the plate. When thus positioned, the combination electrostatic charging and light-projecting mechanism is moved over the plate and copy sheet from right to left of Fig. 2, or the plate and copy sheet may be moved under the charging mechanism and light-projecting means from left to right of Fig. 2, to effect the charging and exposing operations successively.

When the copy sheet is positioned on the plate and corona discharge effected from the needles 2, the electrostatic charge holds the copy sheet tightly against the surface of the plate without requiring an supplemental instrumentalities for making proper contact between the copy sheet and the photoconductive surface. The electrostatic charge at the same time passes through the copy sheet and is imposed on the photoconductive insulating surface ready to receive the image from the copy when light is projected therethrough, and as the charging and exposing operations occur, the plate is continuously charged and exposed successively over given narrow areas of the plate as the relative movement takes place between the plate and charging and exposing mechanism.

While the invention has been described with reference to a particular construction, it is not confined to the details herein shown and this application is intended to cover such modifications or other procedures as may come within the purposes of the improvement or the scope of the following claims.

We claim:

1. The method of producing an electrostatic latent image on an electrophotographic plate which comprises positioning a sheet to be copied over the photoconductive insulating surface of the plate, passing a corona discharge electrode arranged crosswise of the plate over said sheet and plate in a path substantially perpendicular to the electrode to scan the plate and electrostatically charge increments of the plate by corona discharge through said sheet, and then passing a line filament source of light also arranged transversely of the plate over the same path of scanning to discharge said previously charged increments of electrostatic charge on the electrophotographic plate except at the points of the image contained on the sheet to be copied, said electrostatic charge serving to hold the sheet to be copied in contact with the plate while exposing the plate.

2. The method of producing an electrostatic latent image on an electrophotographic plate which comprises positioning a sheet to be copied over the photoconductive insulating surface of the plate, effecting relative movement between said plate and a corona discharge electrode arranged crosswise of the plate in a direction substantially perpendicular to the electrode to scan the plate and electrostatically charg increments of the plate by corona discharge through successive portions of the sheet, and simultaneously exposing previously charged portions of the plate to light projected through the sheet from a line filament source arranged transversely of the plate to discharge said increments of electrostatic charge on the electrophotographic plate except at the points of the image contained on the sheet to be copied, said electrostatic charge serving to hold a sheet to be copied in contact with the plate while exposing the plate.

3. The method of producing an electrostatic latent image on an electrophotographic plate which comprises positioning a sheet to be copied over the photoconductive insulating surface of the plate, passing a corona discharge electrode arranged crosswise of the plate over said sheet and plate in a path substantially perpendicular to theelectrode to scan the plate and electrostatically charge increments of the plate by corona discharge through said sheet, and exposing the sheet and plate to light to discharge said previously' charged increments of electrostatic charge on the electrophotographic plate except at the points of the image contained on the sheet to be copied, said electrostatic charge serving to hold the sheet to'be copied in contact with the plate while exposing the plate.

CHARLES D. OUGHTON. WILLIAM E. BIIKBY.

REFERENCES CITED Date Carlson Sept. 12, 1944 

